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Implanting the Bionic Ear

by Kanon K Roy
***A cochlear implant does not restore a person's hearing to normal. Rather it can provide very useful auditory cues. While the benefits from an implant are not same for everyone, from the experience and case studies, in case of adults, restored detection of everyday sounds in the environment, improved face to face communication, the ability to understand speech through hearing alone, greater confidence to interact and socialize can be expected.***
HEARING impairment in everyday life of an individual results in facing social isolation and medical problems as well as decreased quality of life. Since long hearing aids have proved helpful in cases of moderate deafness and with a few exceptions, in more severe cases. Hearing aids amplify sound to compensate for the loss of sensitivity to sound, but the ability of hearing aids' to separate and selectively amplify different sound frequencies is limited, however. Speech perception becomes difficult in case of severe to profound sensorineural deafness even with the help of most powerful hearing aids available now. With rising noise levels in everyday life specially in cities and areas under industrialization. and aging of the population. the number of people with hearing loss will continue to rise, unfortunately.
Introduction of "Cochlear Implant’ has proved worthwhile in adults and children having severe and profound sensorineural hearing loss who get little or no benefit from hearing aids. Especially in cases of pre-llnguaUy deaf children who have a severe-to-profound sensorineural hearing loss and no memory of speech, hearing aids may not provide adequate benefit even after extensive auditory training. An acquired hearing loss resulting from meningitis or viral Infections can leave a child with total deafness. For this population the cochlear implant Is an alternative to hearing aids, which practically is not a cure for hearing loss and will not restore hearing to normal levels.
Before discussing about the cochlear implant we should know how the ear normally functions In case of a normally functioning ear sound is transmitted as sound waves to the ear-drum causing the latter to vibrate which hi turn causes (he three tiny bones in the middle ear to vibrate. The sound vibrations continue through the middle ear bones and across a tiny membrane to the fluid In the snail-shaped inner ear called cochlea. The movement of fluid in the cochlea causes the movement of numerous hair cells merged into the fluid The movement of the hair cells converts the fluid movement into electrical energy whir l) is iht ii transmitted to the auditory nerve (heating nene) In tin- hair cells. Ilie electrical impulses alter being transmitted to the brain through auditory nerve are Interpreted as sound information there.
In the case of sensorineural deafness the inner ear is dam-
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aged or the hair cells in the cochlea are not developed properly or remain inactive. Hearing aids and other assistive listening devices simply amplify-sound. A cochlear implant, on the other hand, is an electronic device designed to provide useful sound information by directly stimulating the surviving auditory' nerve fibres in the cochlea.
Cochlear implant was first developed in Australia and was first introduced in the 1970’s to enable posl-lingually deafened adults to perceive speech by electrically stimulating their auditory nerve. The first child was implanted with a single channel device in 1980 and prior to this, extensive studies were done on adults to determine its benefit Scientists in this field were engaged to improve the device and five years later, the first child was implanted with a multi-channel cochlear implant. Considerably. better results were obtained for speech production and by 1990, deaf children over two years of age were considered to be candidates for Implantation. All cochlear implant devices have been tested extensively before their use on children not only to determine their benefit for speech and language perception and production. but to ensure that the components of the device would be completely safe also.
Even after the introduction of cochlear implant scientists were working hard to improve the device. Normally functioning cochlea mechanically sorts the sounds according to their frequency and based on this fact multiple electrodes came into consideration and accordingly multi-channel Implant (22 channel) was introduced (he result of which was significantly Improved Development of newest speech coding strategy along with latest 24-channel Implant has been proved spe-' tally worthy in the case of pre-Imgualh deaf children for their speech and language development However, m the case of a cochlear Implant rehabilitation measures i.e. mapping and a< me auditory training aie la< tors toward success .uni realistic expectation from an implant r< • q>n nt <>r parrnis of r < ipn nt is .dso important
There are several brand's ol cochlear implant in use all over the world; for example, Niu lens’. ’Clarion', "Combi 40/40+’ etc. But the most widely used brand is Nucleus' manufactured by Cochlear Ltd. But the basic components of all brands are almost same which are described below briefly.
Components of Cochlear Implant: Multi-channel cochlear Implant consists of 2 main components:
1) The implant package and electrode array (or receiver-stimulator). and
2) The speech processor and headset.
The receiver-stimulator contains the electronic circuits that control the flow of electrical pulses into the ear. an antenna that receives the radiofrequency signal from the external coil and a magnate that holds the externa] coil in place. There are wire leads attached to the package that join to electrodes. The 22- or 24-e!ectrode array is inserted into the snail shaped cociilea and the whole receiver stimulator package is placed under the skin of (he patient behind the ear during implant surgery.
Candidacy for Cochlear Implant: To determine the suitability of each prospective candidate, patient lias to face the pre-operative selection procedure. A number of assessments ire required for this and the re-suits of these tests also allow die clinicians to advise the candidates on the benefit they
may gain f?om the device, 'a team of specialists' i.e., audiologist. otologists, speech pathologists. neurologists, social workers and educationalists will have input into the management of patients.
The plain and simple question is ” who can be benefited from cochlear implant?" The
answer is the same as the sum-maiv o| the selec tion criteria of a probable candidate, which are as follows:
i) The candidate will be at least 12 months of age or older al the time of surgery
ii) The candidate must have little or no hearing In both the ears.
Hi) The candidate must gain little or no benefit from hearing aids.
Iv) The ears must be free of infection.
v| The inm i ear must hi prop* 11\ loi lie d .Did the ,ni(li-tory (hearing) nerve must be intac t.
vl| The candidate must be medically suitable to undergo an operation.
In addition the candidate and/or his family must have realistic expectations from and be aware of the device.
Implantation Surgery: Surgery is needed to insert the electrode array into the cochlea and to anchor the receiver-stimulator package In the temporal bone in the skull. Allot raising the skin from the skull behind the car the surgeon drills in the temporal bone to have access to the cochlea and
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then making a small hole in the wall of the cochlea, he gently guides the electrode array into the shell-like cochlea. Once the array is fixed in place, the wound is closed. Typically the surgery takes 2 to 3 hours and the hospital stay is normally 2 to 3 days.
Fitting of External Components and Rehabilitation Measures: The headset and speech processor are normally fitted 4-6 weeks after the surgery in case of adults. The audiologist sorts out soft and comfortable listening levels for each of the electrodes and uses this information to create a MAP or programme and the fitting process generally continues over several days. In case of children, ihe fitting procedure continues over a 3-month period. Young children are typically monitored 2 to 3 times a week in the first month and 1 or 2 times a week in next 2 months to obtain a stable MAP. Hearing speech with the implant for the first time may appear somewhat unnatural but over days and weeks it begins to sound familiar People who have no experience of hearing before require longer time to adjust to new sounds. In case of children who never had hearing before, the initial reaction to sound varies. Some may not show response to sound at first. Other children may show surprise, fear. Inquisitiveness, or even happiness. Performance usually continues to improve over lime with extensive auditory and speech training.
Follow-up is also very import.mt ami for adults weekly adjustment of MAP and communication therapy are done for the first month alter fitting. The treatment focuses on auditory training, speech reading, telephone use. music and communication strategies. In case of children, after the initial 3 months period, they are examined every 3 months for the first year and every 6 months lor second and third war. Thereafter the child Is examined annually.
Realistic Expectations after a Cochlear Implant: A CO( Idem implant does not restore a pri son s hearing to normal. Rathvi it ( an provide very useful audi lory cues. While the benefits
from an implant are not same for everyone, from the experience and case studies, in case of adults, restored detection of everyday sounds In the environment. improved face to face communication, the ability to understand speech through hearing alone, greater confidence to interact and socialize can be expected. In case of children the result fs almost the same, although progress may be a lot slower. Clinical data show that 60 per cent of children learn to recognize speech without the aid of lip-reading and improvements in the speech and language skills do occui
Cost of Implantation: No doubt, cost of cochlear implantation including post surgery rehabilitation measures is very-high. although it varies from country' to country and place to place. Of course the cost of implantation is the major part of the programme which stands at approximately 54.000 Australian dollars in Australia. The cost has been sufficiently { lowered in India where it goes up to 5 lacs (Nucleus 22) to 8 lacs (Nucleus 24) Indian rupees. In India the implantation has been introduced a couple of years earlier in collaboration with Cochlear Ltd . Australia (manufacturer of Nucleus.’ the most widely used brand) and implant programme for children has been recently introduced in two centers — Madras ENT Research Foundation. Chennai, and Hinduja Hospital. Mumbai.
In a country like Bangladesh where the common people cannot afford such costly technology'. it becomes difficult to introduce such programmes, apparently. It may appear ambitious to expect that steps may be taken by the government or health and welfare sectors for massive hearing screening programmes for all new born babies. and to provide candidates fit for cochlear implant among them with that device at their own cost. But time lias come to think about this community, at least to provide them with possible subsidies for such surgeries or implants and thus rehabilitating them in society with meaningful lives Government as well as interested promoters from private sectors may come forward and help introduce such programmes and technologies in our country, may be In collaboration with the donors, aid agencies, espe-(tally WHO and the concerned manufactures and companies ol the Cochlear Implant device.
Ihe author is a •John < <>m missioner of Taxes and Mem ber. Executive Committee. Ill-CAKE School, Dhaka